1. Field of the Invention
The present invention relates to a CPP (current perpendicular to the plane) type magnetic sensing element. In particular, the present invention relates to a magnetic sensing element capable of properly performing magnetization control of a free magnetic layer.
2. Description of the Related Art
FIG. 31 is a partial sectional view of the structure of a conventional magnetic sensing element, viewed from the side of the surface facing a recording medium.
Reference numeral 1 denotes a lower electrode, and a first antiferromagnetic layer 2 made of PtMn or the like is arranged on the aforementioned lower electrode 1. A pinned magnetic layer 8 formed from CoFe or the like is further arranged on the aforementioned first antiferromagnetic layer 2, a non-magnetic material layer 4 formed from Cu or the like is arranged on the aforementioned pinned magnetic layer 8, and a free magnetic layer 5 formed from NiFe or the like is further arranged on the aforementioned non-magnetic material layer 4. Second antiferromagnetic layers 6 formed from PtMn or the like are arranged on both edge sections in the track-width direction (the X direction shown in the drawing) of the aforementioned free magnetic layer 5. As shown in FIG. 31, an upper electrode 7 is arranged on the aforementioned free magnetic layer 5 and the second antiferromagnetic layers 6. Insulating layers 9 are inserted between the second antiferromagnetic layers 6 and the upper electrode 7.
Magnetization of the aforementioned pinned magnetic layer 8 is pinned in the Y direction shown in the drawing by an exchange coupling magnetic field between the pinned magnetic layer 8 and the aforementioned first antiferromagnetic layer 2. On the other hand, magnetization of both the edge sections of the aforementioned free magnetic layer 5 is pinned in the direction opposite to the X direction shown in the drawing by an exchange coupling magnetic field generated between the edge sections of the free magnetic layer 5 and the second antiferromagnetic layer 6 arranged thereon. However, magnetization of the middle section of the aforementioned free magnetic layer 5 is weakly brought into the condition of a single domain, so that magnetic reversal can be brought about with respect to an external magnetic field.
The magnetic sensing element shown in FIG. 31 is referred to as a CPP (current perpendicular to the plane) type magnetic sensing element, in which the current flowing from the electrodes 1 and 7 passes through the multilayer film from the first antiferromagnetic layer 2 to the free magnetic layer 5 in the film thickness direction (the Z direction shown in the drawing).
The playback output of the CPP type magnetic sensing element can be increased by reduction in the element size compared with that of a CIP (current in the plane) type magnetic sensing element in which the current flowing from electrodes passes through the multilayer film from the first antiferromagnetic layer 2 to the free magnetic layer 5 in the direction parallel to the film surfaces (the X direction shown in the drawing). Consequently, the CPP type was expected to be able to appropriately respond to the reduction in the element size with a future increase in a packing density.
However, regarding the magnetic sensing element shown in FIG. 31, the following problems were pointed out.
FIG. 32 is a partial plan view of portions of the free magnetic layer 5 shown in FIG. 31 and the second antiferromagnetic layer 6 arranged thereon, viewed from directly above.
As shown in FIG. 32, when it is assumed that sense current flows into the central portion of the aforementioned free magnetic layer 5 in the direction opposite to the Z direction shown in the drawing (that is, in the downward direction perpendicular to the paper surface), a sense current magnetic field C is generated following the corkscrew rule at this time. The direction of the aforementioned sense current magnetic field C in a region E on the side of the surface facing a recording medium agrees with the magnetization direction of the free magnetic layer 5 (the direction parallel to the X direction shown in the drawing and the leftward direction in the drawing), and therefore, no problem occurs. However, the direction of the sense current magnetic field in a region D on the back side of the surface facing the recording medium, that is, the rear end surface side, is opposite in direction to the magnetization direction of the aforementioned free magnetic layer 5 (the direction parallel to the X direction shown in the drawing and the rightward direction in the drawing). Therefore, the magnetization of the aforementioned free magnetic layer 5 is likely to be disturbed in this region, and by extension, magnetization control of the total element is hindered.
Since the CPP type magnetic sensing element has a small element resistance, a large playback output cannot be attained unless the sense current density is increased. However, the influence of the aforementioned turbulence in the magnetization of the free magnetic layer 5 is increased with an increase in the aforementioned sense current density. Consequently, hysteresis is exhibited, and degradation of the playback characteristic is brought about.
The aforementioned problems also occur in the case where the magnetization of the aforementioned free magnetic layer 5 is controlled by hard bias layers 63 made of a permanent magnet, arranged on both sides of the aforementioned free magnetic layer 5, in contrast to the magnetic sensing element shown in FIG. 31 and FIG. 32.
FIG. 33 is a partial sectional view of the structure of a magnetic sensing element, in which the magnetization control of the aforementioned free magnetic layer 5 is performed by hard bias layers 63, viewed from the side of the surface facing a recording medium. FIG. 34 is a partial plan view of the aforementioned free magnetic layer 5 and the hard bias layers 63 arranged on both sides thereof, viewed from directly above.
In this magnetic sensing element, a substrate layer 61, a free magnetic layer 4, a non-magnetic material layer 5, a pinned magnetic layer 8, a first antiferromagnetic layer 2 and a protective layer 62 are laminated on a lower electrode 1 in that order. The hard bias layers 63 are oppositely arranged on both sides in the track-width direction (the X direction shown in the drawing) of the aforementioned free magnetic layer 5, and insulating layers 60 formed from Al2O3 or the like are arranged above and under the aforementioned hard bias layers 63.
As shown in FIG. 34, when sense current flows through the aforementioned free magnetic layer 5 in the direction opposite to the Z direction shown in the drawing (that is, in the downward direction perpendicular to the paper surface), a sense current magnetic field C is generated following the corkscrew rule. Consequently, the free magnetic layer 5 magnetized in the direction parallel to the X direction shown in the drawing and the leftward direction in the drawing is affected by the aforementioned sense current magnetic field being directed in the direction opposite to the magnetization direction of the aforementioned free magnetic layer 5 in a region D on the rear end surface side, and therefore, the magnetization of the aforementioned free magnetic layer 5 is disturbed.
When the magnetization control of the aforementioned free magnetic layer 5 is performed using the hard bias layers 63, the aforementioned problems can be alleviated by increasing the film thickness of the aforementioned hard bias layer 63, and thereby enhancing a vertical bias magnetic field in the leftward direction shown in the drawing, which flows into the aforementioned free magnetic layer 5. However, since the aforementioned vertical bias magnetic field becomes excessively strong, the magnetization of the aforementioned free magnetic layer 5 becomes likely to be pinned. Therefore, highly sensitive magnetic reversal is not brought about with respect to an external magnetic field, and a problem of degradation of the playback characteristic occurs.
The aforementioned problem occurs in the case of not only the structure of a magnetic sensing element in which the non-magnetic material layer 4 of the aforementioned magnetic sensing element is formed from a non-magnetic conductive material, for example, Cu, but also the structure of a magnetic sensing element in which the aforementioned non-magnetic material layer 4 is formed from an insulating layer of Al2O3 or the like. A magnetic sensing element having such a structure is referred to as a tunneling magnetoresistance effect type element.